To reduce nitrogen oxide emissions of an internal combustion engine, it is known to convert nitrogen oxide into atmospheric nitrogen and water vapor by means of the selective catalytic reduction (SCR) technology. An aqueous urea solution is used as a reducing agent and is carried in a separate supply vessel. The aqueous urea solution is moved out of the supply vessel by a feed module or a pump and is supplied to a metering module, from which the urea solution is injected in a dosed or metered manner into the exhaust-gas flow upstream of the catalytic converter. Excess reducing agent is conducted by the feed module back into the storage vessel via a return conduit.
Hose conduits for conveying the reducing agent are provided between the supply vessel, the feed module and the metering module. These hose conduits must be connected to the above units to establish the fluid connection. So-called plug-and-socket connections have proven to be advantageous for this purpose since these plug-and-socket connections simplify assembly. The respective hose end is fitted with a plug member or socket member which matches a corresponding plug receptacle on the unit which is to be fluidically connected.
The hose conduits between the supply vessel and the exhaust-gas conduit must be heatable, since there is risk of the aqueous urea solution freezing below −11° C. It is known to avert the risk of freezing by using electrically heatable hoses. Although these electrically heatable hoses have been shown to be effective, there are applications in which this technical solution cannot work, for example, if too little electrical power is available.
It is also possible to arrange a hose conduit, which conducts heating water, in a paired fashion, in close proximity to a hose conduit which conducts reducing agent so as to transfer heat to the latter. The heating water heats the hose conduit conducting the same and transfers the heat energy to the hose conduit conducting the urea solution because of their close proximity. Heating cooling water, which is branched off from the cooling water circuit of the internal combustion engine, can be used as heating water.
With this arrangement, which forms at least one hose conduit pair, freezing of the urea solution in the hose conduits is substantially prevented. There is still the risk of freezing in the plug-and-socket connections themselves. Furthermore, the high number of plug-and-socket connections is disadvantageous, since the hose conduits which conduct heating water must likewise be connected, within their loops, to the units.